1. Technical Field
This invention relates generally to vehicle navigation systems and, more particularly, to simplifying route calculation around traffic obstacles by employing a marked diversion.
2. Related Art
Vehicle navigation systems are becoming increasingly popular in the automobile industry. A typical vehicle navigation system may include a global positioning system (“GPS”) receiver that is mounted somewhere on the vehicle. The GPS receiver is capable of communicating with a satellite-based global positioning system or other localized positioning systems. The GPS receiver obtains geographic position information that is converted into some form of display for the vehicle operator indicating the position of the vehicle relative to previously determined reference points or other known landmarks on a given map database. Other systems and devices may be used to determine the geographic position of the vehicle as well.
The typical vehicle navigation system may also include a digital map database that includes digitized map information that can be processed by a navigation computer designed to handle map-related functions. A map matching module may be used to match the position or trajectory measured by a positioning module to a position associated with a location or route on a map provided from the digital map database. The positioning module may receive its information from the GPS receiver.
The typical vehicle navigation system may also include a human-machine interface module that provides users with a way to interact with the navigation system. A visual display is typically used to convert signals into a visual image in real time for direct interpretation by the user. As such, displays are used to provide optical driver recommendations, which are usually conveyed by a digital map generated on the display. The display itself is typically an electro-optical device such as a liquid crystal display (“LCD”), a cathode-ray tube (“CRT”) display, an electroluminescent display (“ELD”), a heads-up display (“HUD”), a plasma display panel (“PDP”), a vacuum fluorescent display (“VFD”), or a touch-screen display.
A route planning module may also be included that is used to plan a route prior to or during a trip. One commonly used technique is to find a minimum-travel-cost route, which is designed to minimize the amount of distance traveled and the costs associated with reaching a predetermined destination. Other techniques exist that integrate the time one needs if using dedicated roads or may use information about traffic congestion on the route to calculate a route that avoids the traffic congestion. A route guidance module is also included that is used to guide the driver along the route generated by the route planning module. The real time or en-route guidance is typically generated using optical driver recommendations on the display and may also include acoustic driver recommendations.
If traffic congestions or other obstacles are reported along a planned route, the vehicle navigation system will have to find a deviation to the planned route that might require the use of roads of minor importance. For the reason of limited time and memory, it is not possible for a current routing algorithm to check every road to see if it is useful for the best alternative route. The standard search only considers major roads at greater distances from the trip origin and destination and typically only considers smaller roads near the trip origin and destination. As such, if the best alternative route requires a local deviation around an obstacle on smaller roads, the vehicle navigation system should be capable of locating these smaller roads.
Calculation of long trips may be performed by a subdivision of the road network into functional road classes. In the middle of the journey routing techniques as presently implemented on navigation devices only search the most important road connections. These techniques fail to find a recommendable alternative route. Thus, the navigation device may stick to the route as originally calculated deteriorated by one or more traffic obstacles or events.